Allow a boost on particles in MCParticlePairFilter

[cmsbuild]

This change is needed to be able to apply generator-level cuts on momenta in the laboratory frame, instead of the centre of mass frame, in the case of boosted MC production (for proton-lead). Note that this is a different strategy than what was used for 5TeV pPb production (for Run1, in 53X), when a customisation swapping the boost and the filter was used instead (https://github.com/cms-sw/cmssw/blob/CMSSW_5_3_X/GeneratorInterface/HiGenCommon/python/customiseSwapVtxSmearAndProdFilter_cfi.py).
@kurtejung and @mandrenguyen are aware of this pull request.
Let me know if you have any comment on the implementation.
Automatically ported from CMSSW_8_1_X #16425 (original by @echapon).

[cmsbuild]

A new Pull Request was created by @cmsbuild for CMSSW_9_0_X.

It involves the following packages:

GeneratorInterface/GenFilters

@cmsbuild, @govoni, @perrozzi, @thuer, @davidlange6 can you please review it and eventually sign? Thanks.
@agrohsje, @mkirsano this is something you requested to watch as well.
@slava77, @smuzaffar you are the release manager for this.

cms-bot commands are listed here #13028

[perrozzi]

please test

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-any-integration/16371/console

[perrozzi]

please test

[perrozzi]

please test

[cmsbuild]

The tests are being triggered in jenkins.
https://cmssdt.cern.ch/jenkins/job/ib-any-integration/17310/console Started: 2017/01/17 07:31

[cmsbuild]

+1
Tested at: bf9d278
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-16621/17310/summary.html

[cmsbuild]

Comparison job queued.

[cmsbuild]

Comparison is ready
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-16621/17310/summary.html

[perrozzi]

+1

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_9_0_X IBs (tests are also fine). This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @smuzaffar

[davidlange6]

+1
impressive to find a 4-vector class without a boost method - maybe a better one should be used in this class in the future?